Corneal Ulcer and Scar

A corneal ulcer is a defect of the corneal epithelium with underlying inflammation or infection of the stroma; when it heals, the cornea may be left with a scar, an area of permanent opacity. Corneal ulceration and the scarring it leaves behind are major causes of corneal blindness, especially in low- and middle-income regions.

Definition

A corneal ulcer is a localised loss of corneal epithelium with underlying stromal inflammation, infiltrate, or infection; a corneal scar is the residual fibrotic opacity that follows healing of stromal damage.

Scope

This entry covers what distinguishes a corneal ulcer from superficial keratitis, the infectious and non-infectious causes of ulceration, the progression to stromal melt and perforation, and the formation of corneal scar as an endpoint of healing. It is a reference overview and does not provide treatment instructions.

Key concepts

• Epithelial defect with stromal infiltrate
• Infectious versus sterile (immune/neurotrophic) ulceration
• Stromal melt and corneal perforation
• Corneal scar and opacity
• Corneal blindness
• Risk factors: trauma, contact lenses, ocular surface disease

Mechanisms

A corneal ulcer develops when the epithelial barrier is lost and the underlying stroma is invaded by micro-organisms or driven by sterile inflammation. Microbial enzymes and host-derived proteases (collagenases and matrix metalloproteinases) degrade stromal collagen, which can cause progressive thinning, or melt, and in severe cases perforation. As inflammation resolves, fibroblasts lay down disorganised collagen that scatters light, leaving a corneal scar; the location and density of that scar determine its effect on vision. Neurotrophic mechanisms, where impaired corneal innervation prevents epithelial healing, produce persistent non-infectious ulcers.

Clinical relevance

Corneal ulceration is a sight-threatening emergency, and corneal scarring is a leading cause of avoidable blindness worldwide; recognising the features that separate infectious from sterile ulcers informs ophthalmic evaluation. This entry is for reference and study only and is not a basis for diagnosis or treatment.

Epidemiology

Corneal ulceration is most often a sequel of microbial keratitis, so its burden mirrors that of keratitis: high in tropical and agricultural settings, where ocular trauma and fungal infection are common, and increasingly linked to contact-lens wear in high-income settings. Corneal opacity from healed ulceration is recognised as a significant global cause of unilateral blindness.

Debates

Preventing scar to preserve vision

Because the visual outcome of an ulcer depends largely on whether central scarring forms, debate continues over how best to limit stromal melt and scarring, an area where evidence on adjunctive measures remains incomplete.

Seminal works

• ung-2019
• brown-2021-fungal

Frequently asked questions

What is the difference between a corneal ulcer and a corneal scar?

A corneal ulcer is an active, open defect of the corneal surface with underlying inflammation or infection. A corneal scar is what may remain after an ulcer or stromal injury heals, a permanent opacity that can blur vision if it lies over the visual axis.

What causes corneal ulcers?

Most corneal ulcers result from microbial keratitis, bacterial, fungal, viral, or Acanthamoeba infection, usually after a break in the corneal surface from trauma, contact-lens wear, or ocular surface disease. Some ulcers are sterile, driven by immune disease or loss of corneal nerve function.